If the answer hasn't been said already, I'd like to point out that the leaves is the same size as the ants....So book cover is not to scale? Or is this not what the OP is looking for? (IK, this is a really simple solution)

Let me give it a try. Nothing is wrong! Ants represent hardworking miners or people that are taking care of Bitcoin instead of the mighty bankers and government people that are just looking after their own a**!

Or, have they used bitcoin instead of the blockchain? as the cover refers to "Unlocking Digital Cryptocurrencies" which indicates more than the one currency and bitcoin is just one of the many Cryptocurrencies and if the book is about unlocking Cryptocurrencies then it should perhaps read "Mastering the Blockchain" "Unlocking Digital Cryptocurrencies"